Femtosecond carrier dynamics in graphite

Graphene analogue BCN: Femtosecond nonlinear optical susceptibility and hot carrier dynamics

“…The pump generated carriers thermalize nearly instantaneously by carrier-carrier scattering within first few tens of fs [25], spreading the carrier distribution over a wide range, both above and below the states optically coupled by the pump. The hot carrier population causes absorption saturation not only at the pump photon energy but also at probe photon energies different from the pump (though to a lesser extent) [29]. The magnitude of saturation absorption and hence the change in probe transmission will be smaller for the nondegenerate case as seen for RGO: (∆T/T) max = 6.2x10 -3 in degenerate pump-probe [20] and 1.9x10 -3 in present nondegenerate pump-probe experiments.…”

Structural Preablation Dynamics of Graphite Observed by Ultrafast Electron Crystallography

“…The highly anisotropic transfer of carrier energy to a subset of phonons of the quasi-2D-structure alters the forces between layers which control the time scale and amplitude of structural change. These atomic motions on different time scales for compression, expansion and restructuring determine the degree of the instability, which at sufficiently high fluences reaches that of graphene ablation [7,8], as predicted theoretically [9].Previous optical studies have focused on the carrier dynamics induced by both high [10,11] and low fluence [12] optical excitation, revealing features of the unique phonon excitations in quasi-two-dimensional graphite and the coherent modes involved. In order to resolve details of the structure, diffraction is our method of choice.…”

“…Such selective coupling leads to an efficient excitation of a subset of vibrations [20,21], socalled strongly-coupled-optical-phonons (SCOP), which ultimately decay to yield other vibrations. Because of electron-electron scattering the initial fs carrier excitation acquires a broadening in the energy distribution [10,20], and this distribution relaxes by electron-phonon coupling, leading to SCOP in the case of graphite. The time scale has been estimated to be on the order of 500 fs, for the electronphonon-coupling process, and 5 to 7 ps for the decay of SCOP into other modes [20,21].…”

“…Previous optical studies have focused on the carrier dynamics induced by both high [10,11] and low fluence [12] optical excitation, revealing features of the unique phonon excitations in quasi-two-dimensional graphite and the coherent modes involved. In order to resolve details of the structure, diffraction is our method of choice.…”

Cooling of photoexcited carriers in graphene by internal and substrate phonons

“…Upon fast excitation of graphene carriers with light or other means, the dynamics of the resulting non-equilibrium carrier distribution evolve on a fast time scale and has been extensively studied both experimentally [1][2][3][4][5][6][7][8][9][10][11][12][13] and theoretically [14][15][16] . The relaxation involves an initial fast evolution towards quasi-thermal distribution on a femtosecond timescale via electron-electron collisions 14,15,17,18 , followed by energy transfer to phonons on a longer picosecond timescale.…”